One of Darwin's Evolutionary Theories Has Been Proved By Scientists: 'We Are Standing on the Shoulders of Giants'

More than 160 years after Charles Darwin wrote On the Origin of Species, scientists say they have proved one of his theories right.

Researchers writing in Proceedings of the Royal Society B investigated whether or not subspecies may be an early step towards the formation of a new species—a process known as speciation. Their results suggest that yes, it can—supporting arguments put forward by Darwin in his 1859 work.

Darwin's observations led him to believe that the more species present in a genus, the more variation within those species there will be, writing: "From looking at species as only strongly-marked and well-defined varieties, I was led to anticipate that the species of the larger genera in each country would oftener present varieties, than the species of the smaller genera; for wherever many closely related species (i.e., species of the same genus) have been formed, many varieties or incipient species ought, as a general rule, to be now forming."

A species is defined as a set of animals or plants with similar characteristics and that can breed with one another. We as humans, or Homo Sapiens, are an example.

A subspecies, on the other hand, describe populations within a particular species that may look slightly different and have their own separate breeding ground.

The number of subspecies per species varies considerably. There are 45 known subspecies of red fox but no subspecies of human.

Scientists from Cambridge University, in the U.K., analyzed the relationships between the two, calculating how the number of species per genus and the number of subspecies per species for a number of different animal groups.

Laura van Holstein and Robert Foley used information collected by naturalists to determine the "age" of different species and subspecies to see how they closely they were connected.

They noted a correlation between species variation and subspecies variation. Genera with a higher number of species tended to have species with a higher number of subspecies. This relationship was particularly strong among flying mammals like bats. In comparison, land-based animals showed a positive correlation between species richness and subspecies richness—but this correlation was weaker.

The researchers suggest these differences caused by geographical boundaries, which are harder for land-based animals to overcome. A mountain range or river might create a physical barrier separating animals that move on land but not animals that move in the sky or in water.

"It shows that the relationship between subspecies and species is contingent on terrestriality and physical barriers in the landscape—this confirms long-standing models of speciation by Ernst Mayr, who suggested that species form when a barrier is introduced between populations," lead author Laura van Holstein, a PhD student in Biological Anthropology at the University of Cambridge, U.K., told Newsweek. While subspecies, dismissed by some as "unglamorous units of evolutionary biology," may actually be thought of as an "incipient species."

Charles Darwin
(Original Caption) Charles Darwin 1875, photographed by H.P. Robinson. Scientists say their new theory proves an old Darwin theory on evolution right. Bettmann/Getty

"We are standing on the shoulders of giants," van Holstein said in a statement. "In Chapter 3 of On the Origin of Species Darwin said animal lineages with more species should also contain more 'varieties'. Subspecies is the modern definition. Animal subspecies tend to be ignored, but they play a pivotal role in longer term future evolution dynamics."

She continued: "My research investigating the relationship between species and the variety of subspecies proves that sub-species play a critical role in long-term evolutionary dynamics and in future evolution of species. And they always have, which is what Darwin suspected when he was defining what a species actually was."

Van Holstein hopes the research will help conservation efforts, enabling environmentalists to work out which species require more special attention in order to protect them from extinction.

She explained: "If the way that ecology influences subspecies formation is not uniform across all species and subspecies can become full species in the future, anthropogenic destruction of ecosystems will affect subspecies formation, and consequently possibly the future evolution of species, in different ways."

The article has been updated to include comments from Laura van Holstein.